Variable data printing (VDP) is a form of printing in which elements such as text, graphics and images may be changed from one printed piece to the next, without stopping or slowing down the printing process using information from a database or external file.
In one method, a static document is loaded into printer memory. The printer is instructed, through the print driver or Raster Image Processor (RIP), to always print the static document when sending any page out to the printer driver or RIP. Variable data can then be printed on top of the static document.
A second method is to combine the static and variable elements into print files, prior to printing, using standard software. This produces a conventional (and potentially huge) print file with every image being merged into every page. A shortcoming of this method is that running many very large print files can overwhelm the RIP's processing capability. When this happens, printing speeds might become slow enough to be impractical for a print job of more than a few hundred printed pieces.
A third method is to combine the static and variable elements into print files, prior to printing, using specialized VDP software. This produces print files, such as Portable Document Format (PDF) (see, in particular, PDF/VT of ISO 16612-2:2010), PostScript or Personalized Print Markup Language (PPML), that offer the potential to improve print speed since the RIP need only process static elements once. There are a variety of optimized print output formats currently in use for VDP, including optimized PDF, PPML, Fiery FreeForm, Creo Variable Print Specification (VPS), Optimized PostScript, Xerox Variable Data Intelligent PostScript Printware (VIPP), Swift Native Accelerated Personalization (SNAP), PPML/VDX, Advanced Function Printing/Intelligent Printer Data Stream (AFP/IPDS), and JLYT.
To illustrate the challenge, consider the case of an HP Indigo Digital Press from HP, Inc. The press prints each color separation at a resolution of 812 Dots Per Inch (DPI) (320 Dots Per Centimeter), which translates to around 640 K of image data per square inch. Now, for a print speed in which the printed output sheet moves at around 30 meters per minute, one can appreciate that there is potentially a tremendous amount of data that needs to be communicated to and updated in memory of the press for variable components in a limited timeframe.
For a variety of applications, it is useful to encode a unique machine readable serial number into each printed piece (or small lot of pieces). One way to accomplish this is to encode a barcode localized to one area on the printed piece. This limits the variable component of each printed piece to that area, which is dedicated to contain only the barcode. With the printing of each piece, a new barcode is generated and applied to the piece, using one of the methodologies summarized above. These localized barcodes, however, suffer from the drawback that they are only readable from one location, which makes them more difficult and slower to read. Often, the barcode is obscured and needs to be moved or imaged from many different perspectives to read it. Repeating the barcodes on several distinct locations may ameliorate this drawback somewhat, but it detracts from the aesthetics of the printed object and interferes with other information printed on it.
Advanced digital signaling schemes, such as digital watermarking and variants thereof, enable machine readable information to be woven across the entire surface of each printed piece, while coexisting other visual elements. Digital watermarking may be used to serialize objects, as described in U.S. Pat. Nos. 8,594,364 and 8,355,525, which are hereby incorporated by reference. However, to be economically viable for commercial printing, new technologies are needed for VDP workflows. Digital watermark signaling has the advantage of weaving digital information robustly and imperceptibly over the entire surface of an object. Yet, this advantage presents a potential challenge in that large portions of the image may need to be changed for each printed item, slowing down the press and increasing computational complexity.